Laterally diffused metal oxide semiconductor device and method of forming the same

ABSTRACT

A transistor advantageously embodied in a laterally diffused metal oxide semiconductor device having a gate located over a channel region recessed into a semiconductor substrate and a method of forming the same. In one embodiment, the laterally diffused metal oxide semiconductor device includes a source/drain having a lightly doped region located adjacent the channel region and a heavily doped region located adjacent the lightly doped region. The laterally diffused metal oxide semiconductor device further includes an oppositely doped well located under and within the channel region, and a doped region, located between the heavily doped region and the oppositely doped well, having a doping concentration profile less than a doping concentration profile of the heavily doped region.

TECHNICAL FIELD

The present invention is directed, in general, to the semiconductordevices and, more specifically, to a laterally diffused metal oxidesemiconductor device and method of forming the same.

BACKGROUND

The design of early integrated circuits focused on implementing anincreasing number of small semiconductor devices on a semiconductorsubstrate to achieve substantial improvements in manufacturingefficiency and cost, product size, and performance. The continuingimprovements in the design of integrated circuits over the past fewdecades has been so dramatic and so pervasive in numerous products thatthe effects can be measured in changes in industries.

The design and construction of integrated circuits has continued toevolve in a number of different areas. One area of innovation is acontinuing reduction of feature sizes of semiconductor devices such ascontrol and signal processing devices formed on a semiconductorsubstrate. Another area of innovation is the advent of constructiontechniques to incorporate higher voltage semiconductor devices (alsoreferred to as “higher voltage devices”) having higher voltage handlingcapability such as switches of a power train of a power converter intothe integrated circuits.

An objective of incorporating control and signal processing devices on asemiconductor substrate with the higher voltage devices often encountersconflicting design requirements. More specifically, lower voltages(e.g., 2.5 volts) are employed with the control and signal processingdevices (hence, also referred to as “low voltage devices”) to preventflashover between the fine line structures thereof. A potentialdifference of only a few volts separated by a fraction of a micrometercan produce electric fields of sufficient magnitude to induce locallydestructive ionization in the control and signal processing devices.

When employing the higher voltage devices therewith, it is oftennecessary to sense and switch higher external circuit voltages (e.g.,ten volts or higher) on the integrated circuit. To accommodate thehigher voltage devices on a semiconductor substrate with the control andsignal processing devices, a large number of processing steps areperformed to produce the integrated circuit. Since the cost of anintegrated circuit is roughly proportional to the number of processingsteps to construct the same, there has been limited progress in theintroduction of low cost integrated circuits that include both controland signal processing devices and higher voltage devices such as theswitches of the power train of a power converter.

The aforementioned constraints have been exacerbated by the need toemploy a substantial area of the semiconductor substrate to incorporatemore efficient and even higher voltage devices into an integratedcircuit. Inasmuch as the cost of a die that incorporates the integratedcircuit is roughly proportional to the area thereof, the presence of thehigher voltage devices conflicts with the reduction in area achieved byincorporating the fine line features in the control and signalprocessing devices.

With respect to the type of semiconductor devices readily available,complementary metal oxide semiconductor (“CMOS”) devices are commonlyused in integrated circuits. The CMOS devices such P-type metal oxidesemiconductor (“PMOS”) devices and N-type metal oxide semiconductor(“NMOS”) devices are used as logic devices, memory devices, or otherdevices such as the control and signal processing devices. In additionto the CMOS devices, laterally diffused metal oxide semiconductor(“LDMOS”) devices such as P-type laterally diffused metal oxidesemiconductor (“P-LDMOS”) devices and N-type laterally diffused metaloxide semiconductor (“N-LDMOS”) devices are also commonly used inintegrated circuits. LDMOS devices are generally used for the highervoltage devices in the integrated circuit. In the context of CMOStechnology, the higher voltage devices generally relate to devices thatoperate at voltages above a standard operating voltage for the selectedCMOS devices (e.g., the low voltage devices). For instance, CMOS devicesemploying fine line structures having 0.25 micrometer line widthsoperate at or below about 2.5 volts. Thus, higher voltage devicesgenerally include any devices operating above approximately 2.5 volts.

Integrating the CMOS and LDMOS devices on a semiconductor substrate hasbeen a continuing goal in the field of microelectronics and has been thesubject of many references over the years. For instance, U.S. Pat. No.6,541,819 entitled “Semiconductor Device Having Non-Power Enhanced andPower Enhanced Metal Oxide Semiconductor Devices and a Method ofManufacture Therefor,” to Lotfi, et al., issued Apr. 1, 2003, which isincorporated herein by reference, incorporates non-power enhanced metaloxide semiconductor devices (i.e., low voltage devices) with powerenhanced metal oxide semiconductor devices (i.e., higher voltagedevices) on a semiconductor substrate. While Lotfi, et al. provides aviable alternative to integrating low voltage devices and higher voltagedevices on the semiconductor substrate, further improvements arepreferable in view of the higher voltage handling capability associatedwith the use of higher voltage devices such as with the LDMOS devices inthe power train of a power converter.

In the field of power microelectronics, the CMOS devices may be employedas the control and signal processing devices integral to the controllerof a power converter. As an example, the control and signal processingdevices are employed as low voltage switches and comparators that formportions of the controller of the power converter. The LDMOS devices, onthe other hand, may be employed as the higher voltage devices integralto the power train of the power converter. The higher voltage devicesperform the power switching functions to control the flow of power to,for instance, a microprocessor. The power switches include the mainpower switches, synchronous rectifiers, and other power switches germaneto the power train of the power converter. The power switches can alsobe used for circuit protection functions such as a rapidly actingelectronic version of an ordinary fuse or circuit breaker. Variations ofpower switches include metal oxide semiconductor field effecttransistors (“MOSFETs”) that exhibit low level gate-to-source voltagelimits (e.g. 2.5 volts) and otherwise are capable of handing the highervoltages germane to the power train of the power converter.

To achieve the overall reduction in size, the integrated circuits asdescribed herein should include control and signal processing deviceswith fine line structures having sub micron line widths (e.g., 0.25micrometers) on a semiconductor substrate that operate with lowervoltages to prevent flashover within the integrated circuit. At the sametime, the integrated circuit may incorporate higher voltage devices thatcan conduct amperes of current and withstand voltages of, for instance,ten volts. A benefit of incorporating the low voltage devices and thehigher voltage devices on the semiconductor substrate is that it ispossible to accommodate higher switching frequencies in the design ofthe power processing circuit due to a reduction of parasiticcapacitances and inductances in the integrated circuit.

Accordingly, what is needed in the art is a semiconductor device andmethod of forming the same that incorporates low voltage devices andhigher voltage devices on a semiconductor substrate that overcomes thedeficiencies in the prior art. Additionally, there is a need in the artfor a higher voltage device (e.g., a transistor such as a LDMOS device)that can accommodate higher voltages and is capable of being integratedwith low voltage devices on a semiconductor substrate in an integratedcircuit that may form a power converter or portions thereof.

SUMMARY OF THE INVENTION

These and other problems are generally solved or circumvented, andtechnical advantages are generally achieved, by advantageous embodimentsof the present invention which includes a transistor advantageouslyembodied in a laterally diffused metal oxide semiconductor (“LDMOS”)device having a gate located over a channel region recessed into asemiconductor substrate and a method of forming the same. In oneembodiment, the LDMOS device includes a source/drain having a lightlydoped region located adjacent the channel region and a heavily dopedregion located adjacent the lightly doped region. The LDMOS devicefurther includes an oppositely doped well located under and within thechannel region, and a doped region, located between the heavily dopedregion and the oppositely doped well, having a doping concentrationprofile less than a doping concentration profile of the heavily dopedregion. In one advantageous embodiment, the source/drain includes P-typelightly and heavily doped regions and the oppositely doped well is aN-type well. In accordance therewith, the doped region is a P-type dopedregion having a doping concentration profile less than a dopingconcentration profile of the P-type heavily doped region.

In another aspect, the present invention provides a semiconductor deviceon a semiconductor substrate and a method of forming the same. In oneembodiment, the semiconductor device includes a complementary metaloxide semiconductor (“CMOS”) device and a LDMOS device formed on thesemiconductor substrate. The LDMOS device includes a gate located over achannel region recessed into the semiconductor substrate, and asource/drain including a lightly doped region located adjacent thechannel region and a heavily doped region located adjacent the lightlydoped region. The LDMOS device also includes an oppositely doped welllocated under and within the channel region, and a doped region, locatedbetween the heavily doped region and the oppositely doped well, having adoping concentration profile less than a doping concentration profile ofthe heavily doped region. In a related, but alternative embodiment, theCMOS device includes a source/drain having a heavily doped region with adoping concentration profile different from the doping concentrationprofile of the heavily doped region of the source/drain of the LDMOSdevice.

The foregoing has outlined rather broadly the features and technicaladvantages of the present invention in order that the detaileddescription of the invention that follows may be better understood.Additional features and advantages of the invention will be describedhereinafter which form the subject of the claims of the invention. Itshould be appreciated by those skilled in the art that the conceptionand specific embodiment disclosed may be readily utilized as a basis formodifying or designing other structures or processes for carrying outthe same purposes of the present invention. It should also be realizedby those skilled in the art that such equivalent constructions do notdepart from the spirit and scope of the invention as set forth in theappended claims.

DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present invention, reference isnow made to the following descriptions taken in conjunction with theaccompanying drawings, in which:

FIG. 1 illustrates a block diagram of an embodiment of a power converterincluding a semiconductor decive constructed according to the principlesof the present invention;

FIGS. 2 through 14 illustrate cross sectional views of an embodiment ofconstructing a semiconductor device according to the principles of thepresent invention; and

FIG. 15 illustrates a cross sectional view of another embodiment of asemiconductor decive consrtuced according to the principles of thepresent invention.

Corresponding numerals and symbols in the different figures generallyrefer to corresponding parts unless otherwise indicated. The figures aredrawn to clearly illustrate the relevant aspects of the preferredembodiments and are not necessarily drawn to scale.

DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS

The making and using of the presently preferred embodiments arediscussed in detail below. It should be appreciated, however, that thepresent invention provides many applicable inventive concepts that canbe embodied in a wide variety of specific contexts. The specificembodiments discussed are merely illustrative of specific ways to makeand use the invention, and do not limit the scope of the invention.

The present invention will be described with respect to preferredembodiments in a specific context, namely, a transistor [e.g., embodiedin a laterally diffused metal oxide semiconductor (“LDMOS”) device], asemiconductor device incorporating the LDMOS device and methods offorming the same. While the principles of the present invention will bedescribed in the environment of a power converter, any application thatmay benefit from a transistor that can accommodate higher voltages andis integrable with a low voltage device [e.g., complementary metal oxidesemiconductor (“CMOS”) device] on a semiconductor substrate is wellwithin the broad scope of the present invention.

The advantages associated with incorporating the higher voltage LDMOSdevices with the low voltage CMOS devices facilitate the ongoingincorporation of integrated circuits with higher levels of integrationinto more products such as power converters. For the purposes of thepresent invention higher voltage devices refer to devices that canaccommodate higher operating voltages than the standard operatingvoltages for a referenced low voltage device. As an example and in thecontext of CMOS technology, the higher voltage devices generally relateto devices that operate at voltages above a standard operating voltagefor the selected CMOS devices (e.g., the low voltage devices). Forinstance, CMOS devices employing fine line structures having 0.25micrometer line widths operate at or below about 2.5 volts. Thus, highervoltage devices generally include any devices operating aboveapproximately 2.5 volts. In yet another context, the higher voltagedevices also generally include devices that may exhibit a low levelgate-to-source voltage limit (e.g., 2.5 volts) and, at the same time,can handle drain-to-source voltages above the gate-to-source voltagelimit thereof (e.g., ten volts).

Referring initially to FIG. 1, illustrated is a block diagram of anembodiment of a power converter including a semiconductor deviceconstructed according to the principles of the present invention. Thepower converter includes a power train 110, a controller 120 and adriver 130, and provides power to a system such as a microprocessor.While in the illustrated embodiment, the power train 110 employs a buckconverter topology, those skilled in the art should understand thatother converter topologies such as a forward converter topology are wellwithin the broad scope of the present invention.

The power train 110 of the power converter receives an input voltageV_(in) from a source of electrical power (represented by a battery) atan input thereof and provides a regulated output voltage V_(out) topower, for instance, a microprocessor at an output of the powerconverter. In keeping with the principles of a buck converter topology,the output voltage V_(out) is generally less than the input voltageV_(in) such that a switching operation of the power converter canregulate the output voltage V_(out). A main switch Q_(mn) [e.g., aP-channel metal oxide semiconductor field effect transistor (“MOSFET”)embodied in a P-type laterally diffused metal oxide semiconductor(“P-LDMOS”) device] is enabled to conduct for a primary interval(generally co-existent with a primary duty cycle “D” of the main switchQ_(mn)) and couples the input voltage V_(in) to an output filterinductor L_(out). During the primary interval, an inductor currentI_(Lout) flowing through the output filter inductor L_(out) increases asa current flows from the input to the output of the power train 110. AnAC component of the inductor current I_(Lout) is filtered by the outputcapacitor C_(out).

During a complementary interval (generally co-existent with acomplementary duty cycle “1-D” of the main switch Q_(mn)), the mainswitch Q_(mn) is transitioned to a non-conducting state and an auxiliaryswitch Q_(aux) [e.g., a N-channel MOSFET embodied in a N-type laterallydiffused metal oxide semiconductor (“N-LDMOS”) device] is enabled toconduct. The auxiliary switch Q_(aux) provides a path to maintain acontinuity of the inductor current I_(Lout) flowing through the outputfilter inductor L_(out). During the complementary interval, the inductorcurrent I_(Lout) through the output filter inductor L_(out) decreases.In general, the duty cycle of the main and auxiliary switches Q_(mn),Q_(aux) may be adjusted to maintain a regulation of the output voltageV_(out) of the power converter. Those skilled in the art shouldunderstand, however, that the conduction periods for the main andauxiliary switches Q_(mn), Q_(aux) may be separated by a small timeinterval to avoid cross conduction therebetween and beneficially toreduce the switching losses associated with the power converter.

The controller 120 of the power converter receives a desiredcharacteristic such as a desired system voltage V_(system) from aninternal or external source associated with the microprocessor, and theoutput voltage V_(out) of the power converter. In accordance with theaforementioned characteristics, the controller 120 provides a signal(e.g., a pulse width modulated signal S_(PWM)) to control a duty cycleand a frequency of the main and auxiliary switches Q_(mn), Q_(aux) ofthe power train 110 to regulate the output voltage V_(out) thereof. Anycontroller adapted to control at least one switch of the power converteris well within the broad scope of the present invention. As an example,a controller employing digital circuitry is disclosed in U.S. patentapplication Ser. No. [Attorney Docket No. ENP-001], entitled “Controllerfor a Power Converter and a Method of Controlling a Switch Thereof,” toDwarakanath, et al. and U.S. patent application Ser. No. [AttorneyDocket No. ENP-002], entitled “Controller for a Power Converter andMethod of Controlling a Switch Thereof,” to Dwarakanath, et aL, whichare incorporated herein by reference.

The power converter also includes the driver 130 configured to providedrive signals S_(DRV1), S_(DRV2) to the main and auxiliary switchesQ_(mn), Q_(aux), respectively, based on the signal S_(PWM) provided bythe controller 120. There are a number of viable alternatives toimplement a driver 130 that include techniques to provide sufficientsignal delays to prevent crosscurrents when controlling multipleswitches in the power converter. The driver 130 typically includesswitching circuitry incorporating a plurality of driver switches thatcooperate to provide the drive signals S_(DRV1), S_(DRV2) to the mainand auxiliary switches Q_(mn), Q_(aux). Of course, any driver 130capable of providing the drive signals S_(DRV1), S_(DRV2) to control aswitch is well within the broad scope of the present invention.Additionally, an embodiment of a driver is disclosed in U.S. patentapplication Ser. No. [Attorney Docket No. ENP-003], entitled “Driver fora Power Converter and Method of Driving a Switch Thereof,” toDwarakanath, et al., which is incorporated herein by reference.

According to the principles of the present invention, the main andauxiliary switches Q_(mn), Q_(aux) are power switches that can beincorporated into a semiconductor device proximate control or signalprocessing devices that perform the control functions of the controller120 of the power converter. As mentioned above, the control and signalprocessing devices are typically CMOS devices such as P-type metal oxidesemiconductor (“PMOS”) devices and N-type metal oxide semiconductor(“NMOS”) devices (also generally referred to as a “CMOS device andanother CMOS device,” and vice-versa). The PMOS and NMOS devices mayalso be referred to as P-channel and N-channel MOSFETs, respectively.Lower voltages (e.g., 2.5 volts) are employed with the control andsignal processing devices (hence, also referred to as “low voltagedevices”) to prevent flashover between the fine line structures thereof.The main and auxiliary switches Q_(mn), Q_(aux) of the power train 110and ones of the plurality of driver switches of the driver 130 aretypically formed by LDMOS devices that handle higher voltages (e.g., tenvolts) and hence are referred to as higher voltage devices. Integratingthe control and signal processing devices, power switches and driverswitches on a semiconductor substrate provides opportunities forsubstantial reductions in cost and size of the power converter or otherapparatus employing like devices.

Turning now to FIGS. 2 through 14, illustrated are cross sectional viewsof an embodiment of constructing a semiconductor device according to theprinciples of the present invention. Beginning with FIG. 2, illustratedis a cross sectional view of an embodiment of a partially completedsemiconductor device including shallow trench isolation regions 210constructed in accordance with one or more aspects of the presentinvention. In accordance with standard practices in the semiconductorindustry, various features in this and subsequent drawings are not drawnto scale. The dimensions of the various features may be arbitrarilyincreased or decreased for clarity of the discussion herein and likereference numbers may be employed for analogous features of differentdevices that make up the semiconductor device.

The semiconductor device includes a semiconductor substrate (alsoreferred to as a “substrate”) 215 and grown on a surface thereof is anepitaxial layer (e.g., a P-type epitaxial layer) 216, preferably dopedbetween 1×10¹⁴ and 1×10¹⁶ atoms/cm³. The epitaxial layer 216 may not beneeded, particularly if the substrate 215 is a lightly doped P-type.Although in the illustrated embodiment, the substrate 215 is a P-typesubstrate, one skilled in the art understands that the substrate 215could be an N-type substrate, without departing from the scope of thepresent invention.

The substrate 215 is divided into four dielectrically separated areas toaccommodate, in the illustrated embodiment, four transistors (e.g.,MOSFETs) located thereon. More specifically, the substrate 215 canaccommodate a PMOS device and a NMOS device that operate as low voltagedevices within, for instance, a controller of a power converter (i.e.,the control and signal processing devices). Additionally, the substrate215 can accommodate a P-LDMOS device and a N-LDMOS device (alsogenerally referred to as a “LDMOS device and another LDMOS device,” andvice-versa) that operate as higher voltage devices within, for instance,a power train and driver of a power converter (i.e., the power switchesand driver switches).

The shallow trench isolation regions 210 are formed within the epitaxiallayer 216 of the substrate 215 to provide dielectric separation betweenthe devices implemented on the substrate 215. The shallow trenchisolation regions 210 are formed by masking the substrate 215 and usinga photoresist to define the respective regions therein. The shallowtrench isolation regions 210 are then etched and backfilled with adielectric such as silicon dioxide, silicon nitride, a combinationthereof, or any other suitable dielectric material. Then, the epitaxiallayer of the substrate 215 and the shallow trench isolation regions 210are planarized by a lapping process. The steps of masking, etching,backfilling with the dielectric and lapping are well known in the artand will not hereinafter be described in further detail.

Turning now to FIG. 3, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device including aburied layer (e.g., a N-type buried layer) 220 constructed in accordancewith one or more aspects of the present invention. As illustrated, theN-type buried layer 220 is recessed within the epitaxial layer 216 ofthe substrate 215 in the area that accommodates the P-LDMOS device andthe N-LDMOS device. The N-type buried layer 220 is formed by a deep ionimplantation process (e.g, at a controlled voltage of about 200kiloelectronvolts) of an appropriate dopant specie such as arsenic orphosphorus and results in a doping concentration profile, preferably ina range of 1×10¹⁸ to 1×10²⁰ atoms/cm³. The N-type buried layer 220 ispreferably located approximately one micrometer below a top surface ofthe epitaxial layer 216 of the substrate 215, and is annealed (e.g., at600 to 1200 degrees Celsius) as necessary to provide the properdistribution of the implanted ion specie. A lateral location of theN-type buried layer 220 is controlled by a photoresist mask usingtechniques well known in the art. The steps of masking, ion implantingand annealing are well known in the art and will not hereinafter bedescribed in further detail.

Turning now to FIG. 4, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device including wells(e.g. N-type wells) 225 constructed in accordance with one or moreaspects of the present invention. The N-type wells 225 are constructedwith similar doping concentration profiles employing an ion implantationprocess. The N-type wells 225 are formed in the epitaxial layer 216 ofthe substrate 215 in the areas that accommodate the PMOS device and theP-LDMOS device, and under the shallow trench isolation regions 210 abovethe N-type buried layer 220 (for the P-LDMOS). The N-type wells 225 areformed to provide electrical isolation for the PMOS device and theP-LDMOS device and operate cooperatively with the N-type buried layer220 (in the case of the P-LDMOS device) and the shallow trench isolationregions 210 to provide the isolation.

A photoresist mask defines the lateral areas for ion implantationprocess. After the ion implantation process, the implanted specie isdiffused by annealing the substrate 215 at elevated temperature. Anappropriate dopant specie such as arsenic or phosphorus can be used toform the N-type wells 225, preferably, but without limitation, in aretrograde doping concentration profile with approximately 1×10¹⁷atoms/cm³ in the middle, and a higher doping concentration profile atthe surface as well as at the bottom. The steps of masking, ionimplanting and annealing are well known in the art and will nothereinafter be described in further detail.

A width of the N-type wells 225 may vary depending on the particulardevices and application and, as one skilled in the art knows, may belaterally defined by the photoresist mask. For instance, the N-type well225 above the N-type buried layer 220 does not cover the entire areathat accommodates the P-LDMOS device in the epitaxial layer 216 of thesubstrate 215 between the shallow trench isolation regions 210 thereof.The advantages of forming the N-type well 225 in the epitaxial layer 216of the substrate 215 within a portion of the area that accommodates theP-LDMOS device will become more apparent for the reasons as set forthbelow.

Turning now to FIG. 5, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device including wells(e.g., P-type wells) 230 constructed in accordance with one or moreaspects of the present invention. The P-type wells 230 are formed withsimilar doping concentration profiles by ion implantation process of anappropriate specie such as boron. The P-type wells 230 are formed in theepitaxial layer 216 of the substrate 215 between the shallow trenchisolation regions 210 substantially in the areas that accommodate theNMOS device and N-LDMOS device. A photoresist mask defines the lateralareas for the ion implantation process. After the ion implantationprocess, the implanted specie is diffused by an annealing the substrate215 at an elevated temperature.

Again, an appropriate dopant specie such as boron can be used to formthe P-type wells 230, preferably resulting in a retrograde dopingconcentration profile with approximately 1×10¹⁷ atoms/cm³ in the middle,and a higher doping concentration profile at the top surface as well asat the bottom. The steps of masking, ion implanting and annealing arewell known in the art and will not hereinafter be described in furtherdetail. Analogous to the N-type wells 225, a width of the P-type wells230 may vary depending on the particular devices and application and, asone skilled in the art knows, may be laterally defined by thephotoresist mask. For instance, while the P-type well 230 above theN-type buried layer 220 covers the entire area that accommodates theN-LDMOS device in the epitaxial layer 216 of the substrate 215 betweenthe shallow trench isolation regions 210 thereof, it is well within thebroad scope of the present invention to define the P-type well 230 tocover a portion of the area that accommodates the N-LDMOS device in theepitaxial layer 216 of the substrate 215.

Turning now to FIG. 6, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device including gates240 for the PMOS, NMOS, P-LDMOS and N-LDMOS devices constructed inaccordance with one or more aspects of the present invention. Theprocess of forming the gates 240 is preceded by forming gate dielectriclayer 235 over the epitaxial layer 216 of the substrate 215 of athickness consistent with the intended operating voltage of the gates240. The dielectric material is typically silicon dioxide with athickness of about five nanometers for devices employing about 0.25micrometer feature sizes and operating at low gate voltages (e.g., 2.5volts). Assuming the gate-to-source voltage limit of the P-LDMOS andN-LDMOS devices is limited to a lower voltage (e.g., 2.5 volts) and thePMOS and NMOS devices operate at the same voltage, then the gatedielectric layer 235 can be formed with dimensions as set forth above.Preferably, the gate dielectric layer 235 is constructed with a uniformthickness to provide a gate-to-source voltage rating for the devices ofapproximately 2.5 volts that completely or nearly completely saturatesthe forward conduction properties of the device. Of course, theaforementioned voltage range for the devices is provided forillustrative purposes only and other voltage ranges are within the broadscope of the present invention.

Next, a polysilicon layer is deposited over a surface of the gatedielectric layer 235 and doped N-type or P-type, using an appropriatedoping specie. The polysilicon layer is annealed at an elevatedtemperature to properly diffuse the dopant. A photoresist mask isemployed with an etch to define the lateral dimensions to define thegates 240. The steps of depositing the dielectric and polysiliconlayers, doping, annealing, and patterning are well known in the art andwill not hereinafter be described in further detail. Alternatively, thegates 240 may include a wide range of materials including variousmetals, doped semiconductors, or other conductive materials.Additionally, the gates 240 may have a wide range of thicknesses. Thethickness of the gates 240 may range from about 100 to about 500nanometers, but may be even smaller or larger depending on theapplication.

The underlying gate dielectric layer 235 and the gates 240 are formedusing conventional processes and will not hereinafter be described infurther detail. The conventional processes include, but are not limitedto, thermal oxidation, chemical vapor deposition, physical vapordeposition, epitaxial growth, or other similar process. It is recognizedthat the gate dielectric layer 235 and gates 240 may have differentthicknesses in different areas of the substrate 215 without departingfrom the scope of the present invention.

Turning now to FIG. 7, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device including alightly doped region (e.g., a N-type lightly doped region) 245 of adrain (also referred to as a “N-type lightly doped drain region”) forthe N-LDMOS device constructed in accordance with one or more aspects ofthe present invention. The N-type lightly doped drain region 245 allowsthe N-LDMOS device to accommodate higher voltage operation from thedrain to the source thereof. The N-type lightly doped drain region 245may be formed employing an ion implantation process in connection with aphotoresist mask to define the lateral dimensions thereof. Additionally,an annealing process at elevated temperatures distributes the implantedion specie. The N-type lightly doped drain region 245 is preferablydoped, without limitation, to about 1×10¹⁶ to 1×10 ¹⁷ atoms/cm³. Thesteps of patterning, ion implanting and annealing are well known in theart and will not hereinafter be described in further detail.

Turning now to FIG. 8, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device including alightly doped region (e.g., a P-type lightly doped region) 250 of adrain (also referred to as a “P-type lightly doped drain region”) forthe P-LDMOS device constructed in accordance with one or more aspects ofthe present invention. The P-type lightly doped drain region 250 allowsthe P-LDMOS device to accommodate higher voltage operation from thedrain to the source thereof. The P-type lightly doped drain region 250may be formed employing an ion implantation process in connection with aphotoresist mask to define the lateral dimensions thereof. Additionally,an annealing process at elevated temperatures distributes the implantedion specie. The P-type lightly doped drain region 250 is preferablydoped, without limitation, to about 1×10¹⁶ to 1×10¹⁷ atoms/cm³. Thesteps of patterning, ion implanting and annealing are well known in theart and will not hereinafter be described in further detail.

The N-type and P-type lightly doped drain regions 245, 250 providehigher voltage drains for the N-LDMOS and P-LDMOS devices, respectively.In effect, the N-type and P-type lightly doped drain regions 245, 250form parasitic diodes with adjoining oppositely doped regions, namely,the P-type well 230 and N-type well 225, respectively. The breakdownvoltage of the parasitic diodes is determined by the dopingconcentration profiles, with lighter doping concentration profilesproviding a higher breakdown voltage because the resulting internalelectric fields are distributed over longer distances when the diodesare back biased. It is recognized that the width of the N-type andP-type lightly doped drain regions 245, 250 may be individually variedto alter the breakdown voltage characteristics of the respective N-LDMOSand P-LDMOS devices without departing from the scope of the presentinvention.

Turning now to FIG. 9, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device including gatesidewall spacers 255 about the gates 240 constructed in accordance withone or more aspects of the present invention. The gate sidewall spacers255, which may be formed from an oxide or other dielectric material, aregenerally formed by depositing a nitride followed by an etching process.The material forming the gate sidewall spacers 255 may be the same ordifferent from the dielectric material used for the gate dielectriclayer 235.

Turning now to FIG. 10, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device includingheavily doped regions for the source and drain (often referred toindividually as a “source/drain” and together as a “source/drain andanother source/drain,” and vice-versa) of the NMOS and N-LDMOS devicesconstructed in accordance with one or more aspects of the presentinvention. The heavily doped regions (e.g., N-type heavily dopedregions) 260 for the source and drain of the NMOS device preferably havea different doping concentration profile than the heavily doped regions(e.g., N-type heavily doped regions) 262 for the source and drain of theN-LDMOS device. The N-type heavily doped regions 260 for the NMOS deviceare formed within the P-type well 230 thereof and, as alluded to above,form the source and the drain for the NMOS device. Additionally, theN-type heavily doped regions 262 for the N-LDMOS device are formedwithin the P-type well 230 thereof and, as alluded to above, form thesource and a portion of the drain for the N-LDMOS device. Also, theN-type heavily doped region 262 of the drain for the N-LDMOS device isadjacent the N-type lightly doped drain region 245 thereof.

The N-type heavily doped regions 260, 262 may be advantageously formedwith an ion implantation process using dopant specie such as arsenic orphosphorus. The doping process includes a photoresist mask to definelateral dimensions of the N-type heavily doped regions 260, 262 and anannealing process at elevated temperature to properly distribute theimplanted species. The N-type heavily doped region 260 for the sourceand drain of the NMOS device is doped, without limitation, to be greaterthan about 1×10¹⁹ atoms/cm³. The N-type heavily doped region 262 for thesource and drain of the N-LDMOS device is doped, without limitation, tobe greater than about 5×10¹⁹ atoms/cm³. Incorporating the differentdoping concentration profiles of the N-type heavily doped regions 260,262 for the source and drain of the NMOS and N-LDMOS devices typicallyadds additional processing steps to the design thereof. It should beunderstood, however, that the N-type heavily doped regions 260, 262 forthe source and drain of the NMOS and N-LDMOS devices may incorporate thesame or analogous doping concentration profiles and still be within thebroad scope of the present invention. Inasmuch as the steps ofpatterning, ion implanting and annealing are well known in the art, theprocesses will not hereafter be described in further detail.

Turning now to FIG. 11, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device includingheavily doped regions for the source and drain for the PMOS and P-LDMOSdevices constructed in accordance with one or more aspects of thepresent invention. The heavily doped regions (e.g., P-type heavily dopedregions) 265 for the source and drain of the PMOS device preferably havea different doping concentration profile than the heavily doped regions(e.g., P-type heavily doped regions) 267 for the source and drain of theP-LDMOS device. The P-type heavily doped regions 265 for the PMOS deviceare formed within the N-type well 225 thereof and, as alluded to above,form the source and the drain for the PMOS device. Additionally, theP-type heavily doped regions 267 for the P-LDMOS device are formedwithin the N-type well 225 or in a region adjacent the N-type well 225thereof and, as alluded to above, form the source and a portion of thedrain for the P-LDMOS device. Also, the P-type heavily doped region 267of the drain for the P-LDMOS device is adjacent the P-type lightly dopeddrain region 250 thereof.

The P-type heavily doped regions 265, 267 may be advantageously formedwith an ion implantation process using dopant specie such as boron. Thedoping process includes a photoresist mask to define lateral dimensionsof the P-type heavily doped regions 265, 267 and an annealing process atelevated temperature to properly distribute the implanted species. TheP-type heavily doped region 265 for the source and drain of the PMOSdevice is doped, without limitation, to be greater than about 1×10¹⁹atoms/cm³. The P-type heavily doped region 267 for the source and drainof the P-LDMOS device is doped, without limitation, to be greater thanabout 5×10¹⁹ atoms/cm³. Incorporating the different doping concentrationprofiles of the P-type heavily doped regions 265, 267 for the source anddrain of the PMOS and P-LDMOS devices typically adds additionalprocessing steps to the design thereof. It should be understood,however, that the P-type heavily doped regions 265, 267 for the sourceand drain of the PMOS and P-LDMOS devices may incorporate the same oranalogous doping concentration profiles and still be within the broadscope of the present invention. Inasmuch as the steps of patterning, ionimplanting and annealing are well known in the art, the processes willnot hereafter be described in further detail.

The annealing process described above with respect to FIG. 11 inherentlyanneals the previously doped regions of the semiconductor device aswell. As is well understood in the art, the cumulative time-temperaturefunction for the annealing processing steps is a factor in integratedcircuit design to provide proper “drive-in” of the implanted specie. Thetime period, temperature range and selected steps to perform theannealing processes may vary depending on an application and the desiredresults to form a semiconductor device incorporated into an integratedcircuit. Thus, it is contemplated that the annealing processes may beperformed after each ion implantation process as described herein ordelayed until after several ion implantation processes and still achievethe desired results.

As mentioned above, the N-type well 225 above the N-type buried layer220 does not cover the entire area that accommodates the P-LDMOS devicein the epitaxial layer 216 of the substrate 215 between the shallowtrench isolation regions 210 thereof. In particular, the N-type well 225covers about half of the area that accommodates the P-LDMOS devicethrough a channel region 270 that is adjacent to and extends between theP-type heavily doped region 267 of source and the P-type lightly dopeddrain region 250 of the drain, and under the gate 240 thereof recessedinto the substrate 215 (or the overlying epitaxial layer 216) . In otherwords, the N-type well 225 is located under and within the channelregion 270, and the N-type well 225 and N-type buried layer 220 areoppositely doped in comparison to the P-type lightly and heavily dopedregions 250, 267. For purposes of clarity, the channel region 270 isgenerally defined and well understood to be a conductive region betweenthe source and drain (or the lightly or heavily doped regions thereof)of a transistor that is induced under the gate by a charge thereon.Thus, a doped region (e.g., a P-type doped region) 272 extends betweenthe P-type heavily doped region 267 and the N-type well 225 of theP-LDMOS device and has a doping concentration profile less than a dopingconcentration profile of the P-type heavily doped region 267.

In the illustrated embodiment, the P-type doped region 272 happens to beembodied in the epitaxial layer 216 which has a doping concentrationprofile between 1×10¹⁴ and 1×10¹⁶ atoms/cm³. Employing the epitaxiallayer 216 as the P-type doped region 272 provides an opportunity to omita masking and a processing step in the manufacture of the semiconductordevice. Of course, the epitaxial layer 216 may be omitted and the P-typedoped region 272 may be formed in the substrate 215 (in this case, aP-type doped substrate). In yet another alternative embodiment, theP-type doped region 272 may be formed by an ion implantation processprior to implanting the P-type heavily doped region 267 for the drain ofthe P-LDMOS device. In such a case, the P-type doping material such asboron would be implanted to provide a doping concentration profile lessthan a doping concentration profile of the P-type heavily doped region267. Of course, the P-type doped region 272 may be formed with anydoping concentration profile less than the P-type heavily doped region267 including a doping concentration profile less than the P-typelightly doped drain region 250 and still be within the broad scope ofthe present invention.

Incorporating the P-type doped region 272 into the P-LDMOS deviceincreases a breakdown voltage between the P-type heavily doped region267 and the N-type well 225 of the P-LDMOS device. More specifically, ineffect the P-type doped region 272 forms a parasitic diode with theadjoining oppositely doped N-type well 225. The breakdown voltage of theparasitic diode is determined by the doping concentration profiles, withlighter doping concentration profiles providing a higher breakdownvoltage because the resulting internal electric fields are distributedover longer distances when the diodes are back biased. Thus, the P-LDMOSdevice exhibits a higher drain-to-source voltage handing capability dueto the higher breakdown voltage thereof. Thus, the P-LDMOS device canhandle voltages, without limitation, of ten volts while constructed onthe same substrate 215 as the CMOS devices, namely, the PMOS and NMOSdevices that operate at lower voltages (e.g., 2.5 volts). It should beunderstood that while the doped region has been described with respectto the P-LDMOS device, the principles are equally applicable to theN-LDMOS device and, for that matter, other transistors of analogousconstruction.

Turning now to FIG. 12, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device including asalicide layer (one of which is designated 275) on the gate, source anddrain of the NMOS, PMOS, N-LDMOS and P-LDMOS devices constructed inaccordance with one or more aspects of the present invention. As clearlyunderstood by those skilled in the art, the formation of the salicidelayer 275 refers to deposition of a metal over silicon by a sputteringor other deposition process followed by an annealing process to improvea conductivity of polysilicon or other material and to facilitate theformation of ohmic contacts.

First, a region for salicidation is exposed using a photoresist mask toselectively etch the gate dielectric 235 from the source and drain ofthe NMOS, PMOS. N-LDMOS and P-LDMOS devices. Then, a metal, generallytitanium, is deposited and the substrate 215 is annealed at an elevatedtemperature. During the annealing process, metal in contact with siliconreacts with silicon to form the salicide layer 275. The metal not incontact with silicon remains as metal, which can be etched away, leavingbehind the salicide layer 275. The steps of masking, depositing metal,annealing and etching are well known in the art and will not hereinafterbe described in further detail.

Turning now to FIG. 13, illustrated is a cross sectional view of anembodiment of a partially completed semiconductor device includingdielectric regions 280 for defining metal contacts constructed inaccordance with one or more aspects of the present invention. Thesemiconductor device is illustrated following a masking, deposition andetching of a dielectric layer to define the dielectric regions 280. Thedielectric regions 280 may be formed from an oxide or other suitabledielectric material. The dielectric regions 280 are generally formed byblanket depositing the dielectric layer over the surface of thepartially completed semiconductor device and anisotropically etching thedielectric layer, resulting in the dielectric regions 280. The steps ofdepositing the dielectric layer, masking and etching are well known inthe art and will not hereinafter be described in further detail.

Turning now to FIG. 14, illustrated is a cross sectional view of thesemiconductor device including metal (ohmic) contacts 285 formed overthe salicide layer 275 on the gate, source and drain of the NMOS, PMOS,N-LDMOS and P-LDMOS devices constructed in accordance with one or moreaspects of the present invention. The embodiment illustrates thesemiconductor device following deposition and patterning of a metal(e.g., aluminum) for the metal contacts 285. The masking, etching, andfurther deposition of the dielectric and metal layers may be repeatedseveral times to provide multiple, highly conductive layers andinterconnections in accordance with the parameters of the application.For example, a four level metal interconnection arrangement may beprovided by incorporating several steps to form the multi-level metalcontacts 285. As illustrated, the metal contacts 285 are formed aboutand defined by the dielectric layers 280.

Turning now to FIG. 15, illustrated is a cross sectional view of anotherembodiment of a semiconductor device constructed according to theprinciples of the present invention. Inasmuch as the processing steps toconstruct the semiconductor device illustrated with respect to FIG. 15are analogous to the processing steps described above, the steps in theprocess will not hereinafter be described in detail. The semiconductordevice includes shallow trench isolation regions 310 within a substrate315 (e.g., P-type substrate) to provide dielectric separation betweenPMOS, NMOS, P-LDMOS and N-LDMOS devices. A buried layer (e.g., a N-typeburied layer) 320 is recessed within the substrate 315 in the area thataccommodates the P-LDMOS device and the N-LDMOS device.

The semiconductor device also includes wells (e.g., N-type wells) 325formed in the substrate 315 in the areas that accommodate the PMOSdevice and the P-LDMOS device, and under the shallow trench isolationregions 310 above the N-type buried layer 320 (for the P-LDMOS). TheN-type wells 325 are formed to provide electrical isolation for the PMOSdevice and the P-LDMOS device and operate cooperatively with the N-typeburied layer 320 (in the case of the P-LDMOS device) and the shallowtrench isolation regions 310 to provide the isolation. As illustrated,the N-type well 325 above the N-type buried layer 320 does not cover theentire area that accommodates the P-LDMOS device in the substrate 315between the shallow trench isolation regions 310 thereof. The N-typewell 325 for the P-LDMOS is constructed as such for the reasons as setforth herein.

The semiconductor device includes additional wells (e.g., P-type wells)330 formed in the substrate 315 between the shallow trench isolationregions 310 substantially in the areas that accommodate the NMOS deviceand N-LDMOS device. While the P-type well 330 above the N-type buriedlayer 320 covers the entire area that accommodates the N-LDMOS device inthe substrate 315 between the shallow trench isolation regions 310thereof, it is well within the broad scope of the present invention todefine the P-type well 330 to cover a portion of the area thataccommodates the N-LDMOS device in the substrate 315. The semiconductordevice also includes gates 340 for the PMOS, NMOS, P-LDMOS and N-LDMOSdevices located over a gate dielectric layer 335 and including gatesidewall spacers 355 about the gates 340 thereof.

The N-LDMOS device includes lightly doped regions (e.g., N-type lightlydoped regions) 345 for the source and the drain thereof. The P-LDMOSdevice also includes lightly doped regions (e.g., P-type lightly dopedregions) 350 for the source and the drain thereof. In the presentembodiment and for analogous reasons as stated above, the N-type andP-type lightly doped regions 345, 350 provide higher voltage sources anddrains for the N-LDMOS and P-LDMOS devices, respectively. As a result,not only can the N-LDMOS and P-LDMOS devices handle higher voltages fromthe drain-to-source thereof, but the devices can handle a higher voltagefrom a source-to-gate thereof when the source is more positive than thegate 340. It is recognized that the width of the N-type and P-typelightly doped regions 345, 350 may be individually varied to alter thebreakdown voltage characteristics of the respective N-LDMOS and P-LDMOSdevices without departing from the scope of the present invention.Additionally, the N-type and P-type lightly doped regions may be formedin a manner similar to the respective N-LDMOS and P-LDMOS devicesillustrated and described with respect to FIGS. 2 through 14.

The semiconductor device also includes heavily doped regions (e.g.,N-type heavily doped regions) 360 for the source and drain of the NMOSdevice that preferably have a different doping concentration profilethan heavily doped regions (e.g., N-type heavily doped regions) 362 forthe source and drain of the N-LDMOS device. The N-type heavily dopedregions 360 for the NMOS device are formed within the P-type well 330thereof and, as alluded to above, form the source and the drain for theNMOS device. Additionally, the N-type heavily doped regions 362 for theN-LDMOS device are formed within the P-type well 330 thereof and, asalluded to above, form a portion of the source and the drain for theN-LDMOS device. Also, the N-type heavily doped regions 362 of the sourceand drain for the N-LDMOS device are adjacent the N-type lightly dopeddrain regions 345 thereof.

The semiconductor device also includes heavily doped regions (e.g.,P-type heavily doped regions) 365 for the source and drain of the PMOSdevice that preferably have a different doping concentration profilethan heavily doped regions (e.g., P-type heavily doped regions) 367 forthe source and drain of the P-LDMOS device. The P-type heavily dopedregions 365 for the PMOS device are formed within the N-type well 325thereof and, as alluded to above, form the source and the drain for thePMOS device. Additionally, the P-type heavily doped regions 367 for theP-LDMOS device are formed within the N-type well 325 or in regionsadjacent the N-type well 325 thereof and, as alluded to above, form aportion of the source and the drain for the P-LDMOS device. Also, theP-type heavily doped regions 367 of the source and drain for the P-LDMOSdevice are adjacent the P-type lightly doped drain regions 350 thereof.

In the illustrated embodiment, the N-type well 325 above the N-typeburied layer 320 does not cover the entire area that accommodates theP-LDMOS device in the substrate 315 between the shallow trench isolationregions 310 thereof. In particular, the N-type well 325 is located underand within a channel region 370, and the N-type well 325 and N-typeburied layer 320 are oppositely doped in comparison to the P-typelightly and heavily doped regions 350, 367. Thus, doped regions (e.g., aP-type doped regions; also generally referred to as a “doped region andanother doped region”) 372, 374 extend between the P-type heavily dopedregions 367 and the N-type well 325 of the P-LDMOS device and have adoping concentration profile less than a doping concentration profile ofthe P-type heavily doped regions 367. While the P-type heavily dopedregions 367 preferably have the same doping concentration profiles, itis well within the broad scope of the present invention that the P-typeheavily doped region 367 for the source has a different dopingconcentration profile than the counterpart of the drain. The sameprinciple applies to other like regions of the devices of thesemiconductor device.

In the illustrated embodiment, the P-type doped regions 372, 374 happento be embodied in the substrate 315 which has a doping concentrationprofile between 1×10¹⁴ and 1×10¹⁶ atoms/cm³. Employing the substrate 315as the P-type doped regions 372, 374 provides an opportunity to omit amasking and a processing step in the manufacture of the semiconductordevice. In yet another alternative embodiment, the P-type doped regions372, 374 may be formed by an ion implantation process prior toimplanting the P-type heavily doped regions 367 for the source and thedrain of the P-LDMOS device. Of course, the P-type doped regions 372,374 may be formed with any doping concentration profile less than theP-type heavily doped regions 367.

Incorporating the P-type doped regions 372, 374 into the P-LDMOS devicefurther increases a breakdown voltage between the P-type heavily dopedregions 367 and the N-type well 325 of the P-LDMOS device. The P-LDMOSdevice, therefore, exhibits a higher drain-to-source voltage handingcapability due to the higher breakdown voltage thereof and provides ahigher source-to-gate voltage handling capability when the source ismore positive than the gate 340. It should be understood that while thedoped regions have been described with respect to the P-LDMOS device,the principles are equally applicable to the N-LDMOS device and, forthat matter, other transistors of analogous construction.

Additionally, whereas the P-LDMOS and N-LDMOS devices illustrated anddescribed with respect to FIGS. 2 through 14 are referred to asasymmetrical devices, the P-LDMOS and N-LDMOS devices illustrated anddescribed with respect to FIG. 15 are referred to as symmetricaldevices. In other words, the symmetrical nature of the source and drainof the semiconductor device of FIG. 15 provide for a symmetrical device.Of course, those skilled in the art should understand that thedimensions of the source and drain (including the lightly and heavilydope regions thereof) may vary and still fall within the broad scope ofthe present invention. The semiconductor device also includes metalcontacts 385 defined by dielectric regions 380 formed over salicidelayers (one of which is designated 375) for the gate, source and drainof the PMOS, NMOS, P-LDMOS and N-LDMOS devices.

The development of a semiconductor device as described herein retainsthe fine line structures and accommodates an operation at highervoltages and with higher switching frequencies (e.g., five megahertz).By introducing a doped region(s) between the heavily doped region andoppositely doped well, the LDMOS device exhibits a high voltage handlingcapability from the drain to the source thereof. At the same time, thehigher voltage device is constructed employing a limited number ofadditional processing steps. Moreover, the LDMOS device may exhibit alow level gate-to-source voltage limit (e.g., 2.5 volts) and at the sametime handle drain-to-source voltages above the gate-to-source voltagelimit thereof. Alternatively, the LDMOS device may exhibit a higherlevel source-to-gate voltage handling capability (e.g, five volts) whenthe source is more positive than the gate and at the same time handledrain-to-source voltages above the low level gate-to-source voltagelimit thereof. In other words, the LDMOS device can switch the largercurrents normally associated with a power train of a power converter byappropriately designing selected regions thereof as set forth above.

Thus, a transistor (e.g., a LDMOS device) and related method ofconstructing the same with readily attainable and quantifiableadvantages has been introduced. Those skilled in the art shouldunderstand that the previously described embodiments of the LDMOSdevice, semiconductor device and related methods of constructing thesame are submitted for illustrative purposes only. In addition, otherembodiments capable of producing a higher voltage device such as a LDMOSdevice that can accommodate higher voltages and is capable of beingintegrated with low voltage devices on a semiconductor substrate in anintegrate circuit that may form a power converter or portions thereofare well within the broad scope of the present invention.

In an advantageous embodiment, the LDMOS device and semiconductor devicemay be incorporated into an integrated circuit that forms a powerconverter or the like. Alternatively, the semiconductor device may beincorporated into an integrated circuit that forms another system suchas a power amplifier, motor controller, and a system to control anactuator in accordance with a stepper motor or other electromechanicaldevice.

For a better understanding of integrated circuits, semiconductor devicesand methods of manufacture therefor see “Semiconductor DeviceFundamentals,” by R. F. Pierret, Addison-Wesley (1996); “Handbook ofSputter Deposition Technology,” by K. Wasa and S. Hayakawa, NoyesPublications (1992); “Thin Film Technology,” by R. W. Berry, P. M. Halland M. T. Harris, Van Nostrand (1968); “Thin Film Processes,” by J.Vossen and W. Kern, Academic (1978); and “Handbook of Thin FilmTechnology,” by L. Maissel and R. Glang, McGraw Hill (1970). For abetter understanding of power converters, see “Modern DC-to-DCSwitchmode Power Converter Circuits,” by Rudolph P. Sevems and GordonBloom, Van Nostrand Reinhold Company, New York, N.Y. (1985) and“Principles of Power Electronics,” by J. G. Kassakian, M. F. Schlechtand G. C. Verghese, Addison-Wesley (1991). The aforementioned referencesare incorporated herein by reference in their entirety.

Also, although the present invention and its advantages have beendescribed in detail, it should be understood that various changes,substitutions and alterations can be made herein without departing fromthe spirit and scope of the invention as defined by the appended claims.For example, many of the processes discussed above can be implemented indifferent methodologies and replaced by other processes, or acombination thereof.

Moreover, the scope of the present application is not intended to belimited to the particular embodiments of the process, machine,manufacture, composition of matter, means, methods and steps describedin the specification. As one of ordinary skill in the art will readilyappreciate from the disclosure of the present invention, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

1. A transistor having a gate located over a channel region recessedinto a semiconductor substrate, comprising: a source/drain including alightly doped region located adjacent said channel region and a heavilydoped region located adjacent said lightly doped region; an oppositelydoped well located under and within said channel region; and a dopedregion, located between said heavily doped region and said oppositelydoped well, having a doping concentration profile less than a dopingconcentration profile of said heavily doped region.
 2. The transistor asrecited in claim 1 further comprising an oppositely doped buried layerlocated under said doped region.
 3. The transistor as recited in claim 1wherein said doped region is formed from an epitaxial layer located oversaid semiconductor substrate.
 4. The transistor as recited in claim 1wherein said source/drain includes P-type lightly and heavily dopedregions and said oppositely doped well is a N-type well, said dopedregion being a P-type doped region having a doping concentration profileless than a doping concentration profile of said P-type heavily dopedregion.
 5. The transistor as recited in claim 1, further comprising:another source/drain including a lightly doped region located adjacentsaid channel region and a heavily doped region located adjacent saidlightly doped region; and another doped region, located between saidheavily doped region of said another source/drain and said oppositelydoped well, having a doping concentration profile less than a dopingconcentration profile of said heavily doped region of said anothersource/drain.
 6. The transistor as recited in claim 1 further comprisinga gate dielectric layer underlying said gate and gate sidewall spacersabout said gate, said transistor further comprising metal contactsformed over a salicide layer on said gate and said source/drain.
 7. Thetransistor as recited in claim 1 wherein said transistor is a laterallydiffused metal oxide semiconductor device.
 8. A method of forming atransistor, comprising: providing a semiconductor substrate; forming agate on said semiconductor substrate; forming a source/drain by: forminga lightly doped region adjacent a channel region recessed into saidsemiconductor substrate, and forming a heavily doped region adjacentsaid lightly doped region; forming an oppositely doped well under andwithin said channel region; and forming a doped region between saidheavily doped region and said oppositely doped well, said doped regionhaving a doping concentration profile less than a doping concentrationprofile of said heavily doped region.
 9. The method as recited in claim8 further comprising forming an oppositely doped buried layer recessedinto said substrate.
 10. The method as recited in claim 8 furthercomprising forming an epitaxial layer over said semiconductor substrate,said doped region being formed from said epitaxial layer.
 11. The methodas recited in claim 1 wherein said source/drain includes P-type lightlyand heavily doped regions and said oppositely doped well is a N-typewell, said doped region being a P-type doped region having a dopingconcentration profile less than a doping concentration profile of saidP-type heavily doped region.
 12. The method as recited in claim 8,further comprising: forming another source/drain by: forming a lightlydoped region located adjacent said channel region, and forming a heavilydoped region located adjacent said lightly doped region; and forminganother doped region between said heavily doped region of said anothersource/drain and said oppositely doped well, said another doped regionhaving a doping concentration profile less than a doping concentrationprofile of said heavily doped region of said another source/drain. 13.The method as recited in claim 8, further comprising: forming a gatedielectric layer over said semiconductor substrate; forming gatesidewall spacers about said gate; forming a salicide layer on said gateand said source/drain; and forming metal contacts over said salicidelayer on said gate and said source/drain.
 14. The method as recited inclaim 8 wherein said transistor is a laterally diffused metal oxidesemiconductor device.
 15. A semiconductor device on a semiconductorsubstrate, comprising: a complementary metal oxide semiconductor deviceformed on said semiconductor substrate; and a laterally diffused metaloxide semiconductor device, including: a gate located over a channelregion recessed into said semiconductor substrate, a source/drainincluding a lightly doped region located adjacent said channel regionand a heavily doped region located adjacent said lightly doped region,an oppositely doped well located under and within said channel region,and a doped region, located between said heavily doped region and saidoppositely doped well, having a doping concentration profile less than adoping concentration profile of said heavily doped region.
 16. Thesemiconductor device as recited in claim 15 wherein said complementarymetal oxide semiconductor device includes a source/drain having aheavily doped region with a doping concentration profile different fromsaid doping concentration profile of said heavily doped region of saidsource/drain of said laterally diffused metal oxide semiconductordevice.
 17. The semiconductor device as recited in claim 15 furthercomprising another complementary metal oxide semiconductor device andanother laterally diffused metal oxide semiconductor device on saidsemiconductor substrate.
 18. The semiconductor device as recited inclaim 17 wherein said another complementary metal oxide semiconductordevice includes a source/drain having a heavily doped region with adoping concentration profile different from a doping concentrationprofile of a heavily doped region of a source/drain of said anotherlaterally diffused metal oxide semiconductor device.
 19. Thesemiconductor device as recited in claim 17 wherein said complementarymetal oxide semiconductor device is a P-type metal oxide semiconductordevice and said another complementary metal oxide semiconductor deviceis a N-type metal oxide semiconductor device, said laterally diffusedmetal oxide semiconductor device being a P-type laterally diffused metaloxide semiconductor device and said another laterally diffused metaloxide semiconductor device being a N-type laterally diffused metal oxidesemiconductor device.
 20. The semiconductor device as recited in claim15 wherein said laterally diffused metal oxide semiconductor deviceincludes an oppositely doped buried layer located under said dopedregion.
 21. The semiconductor device as recited in claim 15 furthercomprising an epitaxial layer located over said semiconductor substrate,said doped region being formed from said epitaxial layer.
 22. Thesemiconductor device as recited in claim 15 wherein said source/drainincludes P-type lightly and heavily doped regions and said oppositelydoped well is a N-type well, said doped region being a P-type dopedregion having a doping concentration profile less than a dopingconcentration profile of said P-type heavily doped region.
 23. Thesemiconductor device as recited in claim 15 wherein said laterallydiffused metal oxide semiconductor device, further includes: anothersource/drain including a lightly doped region located adjacent saidchannel region and a heavily doped region located adjacent said lightlydoped region, and another doped region, located between said heavilydoped region of said another source/drain and said oppositely dopedwell, having a doping concentration profile less than a dopingconcentration profile of said heavily doped region of said anothersource/drain.
 24. The semiconductor device as recited in claim 15wherein said laterally diffused metal oxide semiconductor device furtherincludes a gate dielectric layer underlying said gate and gate sidewallspacers about said gate, said laterally diffused metal oxidesemiconductor device further including metal contacts formed over asalicide layer on said gate and said source/drain.
 25. The semiconductordevice as recited in claim 15 wherein said complementary metal oxidesemiconductor device includes a gate with a gate dielectric layerunderlying said gate and gate sidewall spacers about said gate, saidcomplementary metal oxide semiconductor device further including metalcontacts formed over a salicide layer on said gate and a source/drainthereof.
 26. A method of forming a semiconductor device, comprising:providing a semiconductor substrate; forming a complementary metal oxidesemiconductor device on said semiconductor substrate; and forming alaterally diffused metal oxide semiconductor device, including: forminga gate on said semiconductor substrate, forming a source/drain by:forming a lightly doped region adjacent a channel region recessed intosaid semiconductor substrate, and forming a heavily doped regionadjacent said lightly doped region; forming an oppositely doped wellunder and within said channel region; and forming a doped region betweensaid heavily doped region and said oppositely doped well, said dopedregion having a doping concentration profile less than a dopingconcentration profile of said heavily doped region.
 27. The method asrecited in claim 26 wherein forming said complementary metal oxidesemiconductor device includes forming a source/drain having a heavilydoped region with a doping concentration profile different from saiddoping concentration profile of said heavily doped region of saidsource/drain of said laterally diffused metal oxide semiconductordevice.
 28. The method as recited in claim 26 further comprising forminganother complementary metal oxide semiconductor device and forminganother laterally diffused metal oxide semiconductor device on saidsemiconductor substrate.
 29. The method as recited in claim 28 whereinforming said another complementary metal oxide semiconductor deviceincludes forming a source/drain having a heavily doped region andforming said another laterally diffused metal oxide semiconductor deviceincludes forming a source/drain having a heavily doped region, a dopingconcentration profile of said heavily doped region of said source/drainof said another complementary metal oxide semiconductor device beingdifferent from a doping concentration profile of said heavily dopedregion of said source/drain of said another laterally diffused metaloxide semiconductor device.
 30. The method as recited in claim 28wherein said complementary metal oxide semiconductor device is a P-typemetal oxide semiconductor device and said another complementary metaloxide semiconductor device is a N-type metal oxide semiconductor device,said laterally diffused metal oxide semiconductor device being a P-typelaterally diffused metal oxide semiconductor device and said anotherlaterally diffused metal oxide semiconductor device being a N-typelaterally diffused metal oxide semiconductor device.
 31. The method asrecited in claim 26 wherein forming said laterally diffused metal oxidesemiconductor device includes forming an oppositely doped buried layerrecessed into said semiconductor substrate
 32. The method as recited inclaim 26 further comprising forming an epitaxial layer located over saidsemiconductor substrate, said doped region being formed from saidepitaxial layer.
 33. The method as recited in claim 26 wherein saidsource/drain includes P-type lightly and heavily doped regions and saidoppositely doped well is a N-type well, said doped region being a P-typedoped region having a doping concentration profile less than a dopingconcentration profile of said P-type heavily doped region.
 34. Themethod as recited in claim 26 wherein forming said laterally diffusedmetal oxide semiconductor device, further includes: forming anothersource/drain by: forming a lightly doped region located adjacent saidchannel region, and forming a heavily doped region located adjacent saidlightly doped region, and forming another doped region between saidheavily doped region of said another source/drain and said oppositelydoped well, said another doped region having a doping concentrationprofile less than a doping concentration profile of said heavily dopedregion of said another source/drain.
 35. The method as recited in claim26 wherein forming said laterally diffused metal oxide semiconductordevice, further includes: forming a gate dielectric layer over saidsemiconductor substrate, forming gate sidewall spacers about said gate,forming a salicide layer on said gate and said source/drain, and formingmetal contacts over said salicide layer on said gate and saidsource/drain.
 36. The method as recited in claim 26 wherein forming saidcomplementary metal oxide semiconductor device, includes: forming a gatedielectric layer over said semiconductor substrate, forming a gate oversaid gate dielectric layer, forming gate sidewall spacers about saidgate, forming a source/drain having a heavily doped region recessed intosaid semiconductor substrate, forming a salicide layer on said gate andsaid source/drain, and forming metal contacts over said salicide layeron said gate and said source/drain.